1. Field of the Invention
This invention relates to a mobile radio wave receiver with automatic gain control.
2. Description of the Prior Art
A mobile radio wave receiver including an automatic gain control circuit for controlling a gain of a high frequency amplifier is known.
FIG. 3 is a block diagram of such prior art a mobile radio wave receiver.
A reception signal from an antenna 1 is supplied to a high frequency amplifier 2 of which gain is controlled by an automatic gain control circuit 3. An output of the high frequency amplifier 2 is supplied to a frequency conversion circuit 4. The frequency conversion circuit 4 converts the output of the high frequency amplifier 2 into an intermediate frequency signal (IF signal) by one of mixers 42a and 42b supplied with local oscillation signals from local oscillators 41a and 41b and the converted signal is supplied to a demodulation circuit 5. The demodulation circuit 5 including a bandpass filter 6, a demodulation signal generation circuit 7, and a waveform shaping filter generates and outputs a demodulated signal, wherein bandwidths of the bandpass filter 6 and the waveform shaping filter 8 are fixed.
The automatic gain control circuit 3 decreases the gain when the electric field is relatively high to prevent interdemodulation interference.